Print hammer mechanisms for high speed printers



March 25, 1969 LEE ET AL 3,434,413

PRINT HAMMER MECHANISMS FOR HIGH SPEED PRINTERS Filed March 15, 1967Sheet Of 2 uasmr mm KEEN kmxw ATTORNEYS March 25, 1969 R LEE ET AL PRINTHAMMER MECHANISMS FOR HIGH SPEED PRINTERS Sheet i of 2 Filed March 13,1967 Di m e E O W M wum T N o M w; a w me United States Patent 3,434,413PRINT HAMMER MECHANISMS FOR HIGH SPEED PRINTERS Ronald Henry Lee,Stevenage, and Albert John Keen,

Letchworth, England, assignors to International Computers and TabulatorsLimited, London, England, a British company Filed Mar. 13, 1967, Ser.No. 622,604 Claims priority, application Great Britain, Jan. 6, 1967,907/67 Int. Cl. B411 9/00 US. Cl. 10193 8 Claims ABSTRACT OF THEDISCLOSURE A multiple print hammer assembly built up by assemblingindividual print hammer assemblies into a trough-shaped alignment memberis disclosed, the hammer assemblies being suitable for use inconjunction with so-called on-the-fiy printing apparatus. Eachindividual print hammer assembly uses a unitary structure to form anintegrated magnetic circuit in conjunction with an armature having anextension having the print hammer itself and electromagnet coils mountedon projections from the structure. Forwardand back-stops are provided.The alignment member may form a heat sink for all the individual hammerassemblies mounted on it. Electrical connections for the energisation ofthe electromagnet coils are provided by contact pins extending from theunitary structure and the pins are also used for the purpose of locatingthe individual hammer circuit in the alignment members. For high speedoperation the armature may be supported on a low-friction bearing, forexample a bearing of polytetrafiuoroethylene, and the armature biassingspring may be separated from the stud upon which it bears by a resilientpad or a pad of low friction material. The forward stop, which isadjustable to limit the travel of the print hammer in response tooperation of the armature, may be separated from the print hammer by apad of resilient material.

Cross-reference to related application The apparatus disclosed herein isalso disclosed, in part, in co-pending patent application No. 621,885filed Mar. 9, 1967, filed by the same inventors and assigned to the sameassignee as the present application.

Background of the invention The present invention relates to printingapparatus of the so-called on-the-fiy kind and in particular to printhammer mechanisms suitable for use in conjunction with printers in whicha type carrier carrying a repertoire of characters is movable past aprinting position and in which a particular character is selected to beprinted by the timed operation of a print hammer.

It has previously been proposed to provide on-the-fiy printing apparatusin which a record member, such as a document is positioned adjacent aprinting member having, for example, a group of rotating typewheels eachcarrying a repertoire comprising a sequence of different characters. Atransfer medium, such as a typewriter ribbon is interposed between thetypewheels and the document, and a group of print hammers, one for eachprint wheel, is provided on the opposite side of the document from thetransfer medium. By selectively energising electromagnets associatedrespectively with the hammers in timed relationship to the rotation ofthe typewheels, the hammers are impelled towards the typewheels so thatcharacters carried by the typewheels are caused to be printed on thedocument, a particular character from any 3,434,413 Patented Mar. 25,1969 In accordance with the present invention an individual print hammerassembly has a unitary magnetic structure supporting energising coilsand a pivot carrying an armature, the armature having an extensioncarrying the print hammer proper. The armature is normally biassed to anon-operated position by spring means but is moved to an operatingposition by the application of an electrical pulse to the coils, therebymomentarily moving the print hammer to an operative position, the extentof movement of the hammer being limited by a front stop. This form ofconstruction provides a highly efiicient magnetic circuit for high speedoperation of the print hammer.

A multiple print hammer assembly is built up by assembling a number ofthe individual print hammer assemblies into an aligning member, eachindividual assembly carrying means for locating it in the requiredposition in the aligning member. Using this form of structure, theindividual print hammer assemblies are secured in position in goodthermal contact with the aligning member which then serves as a heatsink to aid in dissipating heat generated by the electrical impulsesapplied to the coils, thus allowing high current pulses to be used forthe operation of the individual print hammers. In addition the meanscarried by the individual assemblies for locating the assemblies in thealignment member also provides electrical contacts for the supply ofenergising pulses to the electromagnet coils.

Further refinements of construction which assist in enabling high speedoperation of print hammers in assemblies made in accordance with thisinvention include: a low friction bearing for the armature, a resilientor low friction pad interposed between the armature spring and thatparticular member against which it works and a resilient pad interposedbetween the front stop and the print hammer.

view of a group of print hammer assemblies and their operationalrelationship.

Description of the preferred embodiments Referring now to FIGURE 1, aprint hammer assembly has a unitary structure 1 of magnetic material.The unitary structure 1 comprises a foot portion 2, a head portion 3spaced away from the foot portion 2 and a web 4 joining the foot andhead portions 2 and 3. The general configuration of the structure 1 issuch that the web 4 is arranged at one end of the foot and head portions2 and 3 so that these portions both extend from the web in the samedirection. The web 4 is thinner than the foot and head portions 2 and 3and has two parallel projections 5 extending into the space between thefoot and head portions 2 and 3. The projections 5 are arranged to formcores for a pair of electromagnet coils 6.

Each coil 6 is formed by a winding about a thin paper former 7, thewinding and former 7 being encapsulated in an epoxy resin after thewinding has been completed, so that an entire coil is slid over one ofthe projections 5. The windings are connected in series by conventionalflying leads from the coils to a pair of contact pins 8. The contactpins are held in the foot portion 2 of the unitary structure 1 and areelectrically insulated from the structure 1 by means of insulatingsleeves 9, the pins 8 projecting beyond the sleeves 9 outside the footportion 2 of the structure 1.

A block 10 is secured by means of a screw 11 to the head portion 3 ofthe unitary structure 1. The block 10 carries a pivot pin 12, and anarmature 13 is supported by the pivot pin 12. The armature is arrangedso that in operation it is attracted in response to energisation of themagnet coils 6 to move to a position bridging the ends of theprojections 5. An extension 14 is provided on the armature 13 and aprint hammer 15 is mounted on the end of the extension 14. The extension14 is arranged generally at right angles to the direction in which thearmature 13 extends, so that the extension lies within the space betweenthe foot and head portions 2 and 3. The print hammer is shaped so thatits extremity projects above and at one end of the head portion 3 asshown in the figure, and is moved by movement of the armature 13 intothe bridging position so that this projection is increased. The headportion 3 of the unitary structure 1 carries a screw 16 which ispositioned so that it limits this movement of the print hammer 15. Thus,the screw 16 forms an adjustable front stop for the print hammer.

The armature 13 is biassed by means of a spring member 17 so that it isnormally maintained in a non-operated position spaced away from the endsof the projections 5 by a small distance. The spring member 17 is a fiatspring secured by means of a block 18 to one end of the armature 13. Thefree end of the spring 17 acts against a stud 19 in the web 4 of theunitary structure 1.

As shown in FIGURE 3, a multiple print hammer assembly is built up byaligning a group of the assemblies described above in side-by-siderelationship so that the extremities of all the print hammers 15 arearranged in line. A further group of assemblies are similarly mutuallyaligned and the two groups are arranged with respect to each other sothat the print hammers of the first group are interleaved between thoseof the second group, thus forming a single line of print hammers. Inorder to prevent stray magnetic fields from one hammer assembly fromaffecting adjacent assemblies, each assembly carries a shield 20 ofmagnetic material (FIGURES l and 3). The shield 20 is convenientlysupported by an adhesive layer applied to the outer surface of themagnetic coils 6.

In order to maintain the individual print hammer assemblies in positionin the multiple assembly an aligning member 21 is provided. The aligningmember is generally trough-shaped and has locating holes 22 provided inthe base of the trough to accommodate the connecting pins 8 and theirinsulating sleeves 9, the pins 8 projecting through the base of thetrough. The print hammer assemblies are secured in the aligning memberby screws 23 and 24, the screw 23 passing through a hole 25 in the baseinto the foot portion 2 of the unitary structure 1 of the assembly andthe screw 24 passing through a hole in the head portion 3 into athreaded hole 26 in the aligning member 21.

A series of resilient members 27 are provided arranged along the innersides of the member 21, each of the members 27 being positioned adjacentone of the armatures. Each of the members 27 is arranged to form abackstop for the armature with which it is associated when thecorresponding individual print hammer assembly is secured into positionin the trough.

In operation, the multiple print hammer assembly consisting of a numberof individual hammer assemblies secured to the aligning member, issupported in relation to a conventional rotary type carrying member,such as a group of print wheels each carrying a repertoire ofcharacters. The arrangement is such that the characters of a singlewheel are carried in turn past a print hammer so that a single characteris selected to be printed b the timed operation of the print hammer inthe conventional manner. It will be appreciated that as the speed ofrotation of the typewheels is increased, the time available for theoperation of a print hammer is decreased, and it becomes necessary toincrease the speed of response and of operation of the print hammer inorder to allow a selected character to be printed cleanly and in correctposition on a document. The present print hammer assembly, as describedabove employs an integral magnetic circuit in which the yoke and themagnet cores and pole pieces are all parts of the single unitarystructure 1 to provide improved magnetic characteristics. This form ofconstruction provides a high efiiciency magnetic circuit of small size,and since the size is reduced the mass of moving parts may also bereduced, thus allowing faster operation.

The speed of response and operation of the print hammer may also beimproved by the use of relatively high energising current pulses appliedto the magnet coils 6. However, because the increase in speed ofrotation of the typewheels may involve a shorter cycle of operation ofthe apparatus, the frequency with which operating pulses are applied tothe magnet coils also increases. The combined effects of high energisingcurrent and faster pulse repetition rate tends to produce an undesirablerise in temperature in the magnet coils 6. In the present apparatus, theuse of a thin former 7, preferably of paper, on which the operatingcoils are wound allows the rapid transfer of heat to the unitarystructure 1. By arranging that the meeting faces of the unitarystructure and the aligning member 21 are machined to provide a goodthermal contact and by making the aligning member of heavy and robustconstruction, the aligning member provides a heat sink, so that theundesirable local temperature rise in the operating coils of theindividual hammer assemblies is greatly reduced.

It is also to be noted that the use of the contact pins 8 and theirassociated insulating sleeves 9 to locate the individual print hammerassemblies in the aligning member 21 enables a multiple hammer assemblyto be built up without the use of conventional spacer combs to separatethe individual print hammers, thus reducing the risk that the hammersmay touch the combs with a consequent deterioration in speed of responseas well as providing a simpler, more easily assembled, and thereforeless costly, unit.

The print hammer assembly shown in FIGURE 1 may be modified to furtherimprove its performance, as shown in FIGURE 2. The pivot pin 12 is, inthis case, enclosed in a sleeve 28 of a material having a very lowcoeflicient of friction, such as polytetrafluorethylene. The sleeve 28then forms a low-friction bearing for the armature 13. The armaturespring member 17 is separated from the stud 19 carried by the unitarystructure 1 by resilient pad 29. The pad 29 serves to damp out anymechanically induced vibration in the spring which might adverselyoffset the performance of the assembly. The pad 29 may 31- ternativelybe formed from a low-friction member to avoid any frictional lossescaused by the spring 17 rubbing the stud 19 carried by the unitarystructure 1 by a resilient 15 to bounce on the front stop screw 16, thescrew 16 may be separated from metallic contact with the print hammer 15by a further resilient pad 30.

We claim:

1. A print hammer assembly including a unitary structure of magneticmaterial having a pair of projections;

a magnet coil about at least one of said projections, the coilcomprising a winding upon a thin former so d1mensioned to fit closelyabout the projection;

a pivot;

means for supporting the pivot, the supporting means being secured tosaid unitary structure;

an armature supported by said pivot and operable in response toenergisation of said coil to move towards a position bridging saidprojections;

spring means between said unitary structure and said armature acting tobias the armature toward a nonoperated position spaced away from saidprojection; an extension on the armature; a print hammer carried by saidextension;

an adjustable front stop carried by said unitary structure to limitmovement of said print hammer produced by movement of said armaturetowards said bridging position; an aligning member having an apertureand means for locating said unitary structure relative to the aligningmember including a locating member carried by said unitary structure andengaging in the aperture in the aligning member, an electrical conductorextending through the cating member and electrically insulated from saidunitary structure and from said aligning member, and an electricalconnection between said electrical conductor and said magnet coil. 2. Aprint hammer assembly as claimed in claim 1 in which the locating meansincludes a pair of electrically conductive pins, and a sleeve ofinsulating material surrounding at least one of said pins. 3. A printhammer assembly including an aligning member; a plurality of unitarystructures of magnetic material,

each structure having a pair of projections; means on each unitarystructure for locating the respective structures relative to thealigning member; means for securing each said unitary structure to saidaligning member in thermally conductive relationship with said aligningmember, the aligning member being effective as a heat sink for all saidunitary structures; each said unitary structure carrying a magnet coilabout at least one of said projections, the coil comprising a windingupon a thin former so dimensioned to fit closely about the projection; apivot; means for supporting the pivot on the unitary structure; anarmature supported by said pivot and operable in response toenergisation of said coil to move towards a position bridging theprojections; spring means acting between said unitary structure and saidarmature to bias the armature toward a non operated position spaced awayfrom the projections; an extension on the armature; a print hammercarried by said extension and an adjustable front stop carried by saidunitary structure and arranged to limit movement of said print hammerproduced by movement of said armature towards the bridging position. 4.A print hammer assembly including an aligning member; a unitarystructure of magnetic material having a pair of projections;

means on said unitary structure for engaging the aligning member tolocate the structure relative to the aligning member and to secure theunitary structure to the aligning member;

a magnet coil about at least one of said projections, the coilcomprising a winding upon a thin former so dimensioned to fit closelyabout the projection;

a pivot .pin;

means for supporting the pivot pin on the unitary structure;

an armature supported by said pivot pin for rotation about alongitudinal axes of the pivot pin, said armature being responsive toenergisation of said coil to rotate in a first direction towards aposition bridging said projections;

spring means acting between said unitary structure and said armaturetending to rotate the armature in a direction opposite to said firstdirection away from said projections;

an extension on the armature;

a print hammer carried by said extension and an adjustable front stopcarried by said unitary structure effective to limit movement of saidprint hammer produced by rotation of the armature in the firstdirection.

5. A print hammer assembly as claimed in claim 4 including a stud onsaid unitary structure and in which said spring means comprises a leafspring secured at one end to said armature, the opposite end of the leafspring engaging the stud.

6. A print hammer assembly as claimed in claim 5 in which the oppositeend of the leaf spring includes a pad of resilient material whichengages the stud on the unitary structure.

7. A print hammer assembly as claimed in claim 4 including a member oflow friction material rotatable about said pivot pin and in which thearmature is supported on said member.

8. A print hammer assembly as claimed in claim 4 in which the adjustablefront stop includes an element of re silient material arranged to engagethe print hammer to limit the movement of the print hammer in the firstdirection.

References Cited UNITED STATES PATENTS 2,940,385 6/1960 House 101-933,110,250 11/1963 Fradkin 101-93 3,177,803 4/1965 Antonucci 101-933,183,830 5/1965 Fisher et a1. 101-93 3,200,739 8/ 1965 Antonucci 101-933,266,418 8/1966 Russo 101-93 3,314,359 4/1967 Martin 101-93 3,349,69610/ 1967 Potter 101-93 WILLIAM B. PENN, Primary Examiner.

